Flux ring for an electric motor

ABSTRACT

A flux ring for a motor of a power tool has an annular housing which fits inside the motor can of the motor. At least one magnet is on the ring. The at least one magnet includes a portion formed from an isotropic magnetic material and a portion formed from an anisotropic magnetic material. Preferably, the isotropic magnetic material is sandwiched by the anisotropic magnetic material. The magnets being molded onto the flux ring in a two shot process.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to AC and DC motors and, moreparticularly, to flux rings for the motors.

[0002] In order to improve motor performance, Rare Earth magnet such asInjection Bonded Neodymium-Iron-Boron (N.I.B.) magnet is used. However,the rated operating temperature of the Injection Bonded N.I.B. magnet istypically in the range of 120° C. Thus, the power tool can be operatedonly up to this limited temperature. Also, the Injection Bonded N.I.B.magnet, particularly the isotropic N.I.B. magnet, is very hard tomagnetize radially. The material costs increase dramatically whenanisotropic material which enables radial magnetic field orientation isused.

[0003] The present invention provides the art with motor magnets whichprovide increased thermal performance. The magnets are also easier tomagnetize such that the radial components of the magnets are directed tothe center of the flux ring. Also, the magnets are cost-effective.

[0004] According to a first aspect of the invention, a flux ring for amotor comprises a ring which fits inside a motor can of the motor. Atleast one magnet is positioned on the ring. The at least one magnetincludes a portion formed from an isotropic magnetic material and aportion formed from an anisotropic magnetic material. Generally, bothmagnets are formed from the isotropic and anisotropic materials. Theisotropic as well as anisotropic materials are magnetic powders. Also,the isotropic and anisotropic magnetic materials are in a resin whichenables the material to be injection molded onto the ring. The isotropicmagnetic material portion is sandwiched between two anisotropic magneticmaterial portions such that the isotropic magnetic material portion ison an arc circle of between 40° and 50°. The magnet itself is on an arccircle of about 140° about the ring. The isotropic magnetic materialportion is generally located on the poles of the motor.

[0005] In accordance with a second aspect of the invention, a method ofmanufacturing a flux ring comprises providing a ring having an anchoringmechanism. Placing the ring in a die. Molding a first isotropic magneticmaterial onto the ring where the anchoring mechanism secures the firstisotropic magnetic material to the ring. Molding a second anisotropicmagnetic material onto the ring adjacent the first isotropic magneticmaterial. The anchoring mechanism secures the second anisotropicmagnetic material to the ring. Further, the anisotropic magneticmaterial is molded on two sides of the first isotropic magneticmaterial. The first isotropic magnetic material is molded without amagnetic field present. The second anisotropic magnetic material ismolded under a magnetic field of about 1400-1600 amp/meter. Also, thefirst isotropic magnetic material is molded along an arc circle of thering along 40° to 50° of the circle. The second anisotropic magneticmaterial is molded along the circle such that the magnet covers about140° of the circle.

[0006] In accordance with a third aspect of the invention, a motorcomprises a stator assembly with the stator assembly including a fluxring. The flux ring comprises an annular housing. At least one moldedmagnet is received on the housing. An anchor mechanism on the housingretains the at least one magnet on the annular housing. At least onemagnet is positioned on the ring. The at least one magnet includes aportion formed from an isotropic magnetic material and a portion formedfrom an anisotropic magnetic material. Generally, both magnets areformed from the isotropic and anisotropic materials. The isotropic aswell as anisotropic materials are magnetic powders. Also, the isotropicand anisotropic magnetic materials are in a resin which enables thematerial to be injection molded onto the ring. The isotropic magneticmaterial portion is sandwiched between two anisotropic magnetic materialportions such that the isotropic magnetic material portion is on an arccircle of between 40° and 50°. The magnet itself is on an arc circle ofabout 140° about the ring. The isotropic magnetic material portion isgenerally located on the poles of the motor. Also, the motor comprisesan armature rotatable within the stator assembly. A commutator isrotatable with the armature and connected to the armature via a shaft. Abrush assembly is associated with the commutator.

[0007] In accordance with a fourth aspect of the invention, a power toolcomprises a housing with a motor in the housing. The motor comprises astator assembly with the stator assembly including a flux ring. The fluxring comprises an annular housing. At least one molded magnet isreceived on the housing. An anchor on the housing retains the at leastone magnet on the annular housing. At least one magnet is positioned onthe ring. The at least one magnet includes a portion formed from anisotropic magnetic material and a portion formed from an anisotropicmagnetic material. Generally, both magnets are formed from the isotropicand anisotropic materials. The isotropic as well as anisotropicmaterials are magnetic powders. Also, the isotropic and anisotropicmagnetic materials are in a resin which enables the material to beinjection molded onto the ring. The isotropic magnetic material portionis sandwiched between two anisotropic magnetic material portions suchthat the isotropic magnetic material portion is on an arc circle ofbetween 40° and 50°. The magnet itself is on an arc circle of about 140°about the ring. The isotropic magnetic material portion is generallylocated on the poles of the motor. Also, the motor comprises an armaturerotatable within the stator assembly. A commutator is rotatable with thearmature and connected to the armature via a shaft. A brush assembly isassociated with the commutator. Also, the power tool includes an outputmember coupled with the motor shaft. An actuator member is electricallycoupled between the motor and the power source to energize andde-energize the motor. In turn, when the motor is energized, the outputmember rotates.

[0008] Additional objects and advantages of the present invention willbecome apparent from the detailed description of the preferredembodiment, and the appended claims and accompanying drawings, or may belearned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 illustrates a cross-section view of a power tool inaccordance with the present invention.

[0010]FIG. 2 illustrates a perspective view of a flux ring in accordancewith the present invention.

[0011]FIG. 3 is a cross-section view through FIG. 2 along line 3-3thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] Turning to FIG. 1, a power tool in accordance with the presentinvention is illustrated and designated with the reference numeral 10.The power tool 10 is illustrated as a drill; however, any type of powertool such as a screwdriver, sander, rotary tool, clippers, saw or thelike which utilize an electric motor may be used with the motor of thepresent invention. The power tool 10 includes a housing 12 whichsurrounds a motor 14. An activation member 20 is coupled with the motor14 as well as with a power source 22. The power source 22 may be a powercord (AC current) or the power tool may have a battery (DC current) asshown. The motor 14 is coupled with an output 16 which may include atransmission 17 and a chuck 18 to retain a tool (not shown) with thedrill.

[0013] The motor 14 includes a stator assembly 30 which includes ahousing 32, flux ring 34, and magnets 36 and 38. An armature 40 includesa shaft 42, a rotor 44 with laminations 46 and windings 48, as well as acommutator 50 coupled with the shaft 42. The motor also includes endplates 52 and 54. End plate 52 includes a bearing 56 which balances oneend of the shaft 58 which is coupled with a pinion 60 which is part ofthe power tool output.

[0014] Brushes 62 and 64 which are associated with the commutator 50. Abearing 70 is also coupled with the end cap to balance rotation of theshaft 42.

[0015] Turning to FIG. 2, the flux ring 34 is illustrated with magnets36 and 38. The magnets 36 and 38 are of a molded magnetic material.Preferably, the molded material is an injection molded material. Thering 34 is positioned within a die and the magnetic material is moldedonto the flux ring. Also, the housing 32 may be used as the flux ring.Thus, the discussion with respect to the ring 34 may equally apply tothe metallic housing 32 of the motor 14.

[0016] The flux ring 34 includes anchors 80 to retain the magnets 36 and38 onto the ring 34. The anchors 80 may be of two types. First, anchor82 is an aperture formed in the housing 34. The aperture 82 has a firstportion 84 and a second counter-sink portion 86. The counter-sinkportion 86 extends to the exterior 88 of the ring 34. Thus, as seen inthe cross-section in FIG. 3, as the molded magnetic material is receivedin the aperture 82, the molded material has a neck 92 and a head 94. Thehead 94 and neck 92 provide an overall rivet appearance, thus the largehead 94 acts to retain the magnet 36, 38 on the ring 34. The ring 34 maybe comprised of just a plurality of aperture anchors 82 to retain themagnets on the ring 34.

[0017] Additional anchors 96 may be utilized on the ring. Anchors 96project from the interior surface 98 of the ring 34. Ordinarily, theanchors 96 are stamped or the like into the ring 34 forming an aperture100 immediately adjacent the projecting anchor 96. Thus, when the moldedmagnetic material forms around the projecting anchor 96, it likewisegoes under the anchor 96 and fills in the aperture 100. This provides afirm securement for the magnet onto the ring 34. For a furtherunderstanding of the flux ring and anchors in accordance with thepresent invention, please see U.S. patent application Ser. No.09/492,059 filed Jan. 27, 2000 entitled “Anchoring System for InjectionMolded Magnets on a Flux Ring or Motor Housing”, and U.S. patentapplication Ser. No. 09/520,471 filed Mar. 8, 2000 entitled “PermanentMagnet Motor Flux Rings”, both of which the specification and drawingsare herein incorporated by reference.

[0018] Turning to the magnets 36 and 38, only one will be describedsince the description relates to both. The magnets 36 and 38 are dividedinto three portions 100, 102 and 104. The portion 100 is sandwichedbetween the portions 102 and 104. The magnet portion 100 is positionedon magnets 36 and 38 along the north and south poles. The magneticportion 100 is along an arc circle of from about 40° to 50°. Themagnetic portion 100 is formed from an isotropic magnetic powdercompound. Also, the magnet includes a resinous material to bring theisotropic compound into an injectionable form. The isotropic magneticpowder compound has a high temperature rating and can be magnetized insitu. Thus, as the isotropic material is magnetized, since the materialstraddles the north and south pole of the magnetizing device, theisotropic material has its magnetic field substantially parallel to thepoles pointing to the center of the flux ring.

[0019] The magnetic portions 102 and 104 are formed from an anisotropicmagnetic powder compound with a desired resin so that they are likewiseinjection moldable. The anisotropic magnetic powder material is mucheasier to magnetize so that the magnet field of the anisotropic magneticmagnet portions 102 and 104 extend radially towards the center of theflux ring as seen by the arrows. The total arc of the arc circle of themagnet with the anisotropic magnetic portions sandwiching each side ofthe isotropic magnetic portion is approximately 140 °.

[0020] A method of manufacturing a flux ring in accordance with theinvention is accomplished by providing the annular housing. The annularhousing within a die wherein the magnets may be injection molded ontothe die. First, the isotropic magnetic portion is molded onto the fluxring and secured onto the flux ring by an anchor as described above. Inthe second step, the anisotropic magnet material is injection molded onboth sides of the isotropic magnetic material sandwiching it in betweenthe two anisotropic magnetic material portions. While the anisotropicmagnetic material is being molded, a magnetic field is present such thatthe anisotropic magnet material is molded in a field of about 1400amp/meter. No field is present during the molding of the isotropicmagnetic material. After molding, a magnetizing mandrel is positionedinside of the flux ring to magnetize the entire can assembly. Afterthis, the magnet is magnetized so that the fields of each magnet ispointing to the center of the flux ring. After the flux ring isproduced, it is welded into a motor can and the above described elementsare added to form a motor. Then the motor would be positioned into thehousing of the power tool.

[0021] While the above detailed description describes the preferredembodiment of the present invention, the invention is susceptible tomodification, variation, and alteration without deviating from the scopeand fair meaning of the subjoined claims.

What is claimed is:
 1. A flux ring for a motor, comprising: a ring forfitting inside a motor can of a motor; at least one magnet on said ring,said at least one magnet including a portion formed from an isotropicmagnetic material and a portion formed from an anisotropic magneticmaterial.
 2. The flux ring according to claim 1, wherein isotropicmagnetic material being an isotropic magnetic powder.
 3. The flux ringaccording to claim 1, wherein said anisotropic magnetic material beingan anisotropic magnetic powder.
 4. The flux ring according to claim 1,wherein said isotropic magnetic material portion is sandwiched betweentwo anisotropic magnetic material portions.
 5. The flux ring accordingto claim 4, wherein said isotropic magnetic material portion spans anarc circle of between 40° and 50° about said ring and said isotropic andtwo anisotropic magnetic material portions span about 140° about saidring.
 6. The flux ring according to claim 5, wherein said isotropicmagnetic material is located on one of the poles of a motor.
 7. The fluxring according to claim 6, wherein one end is connected to said housing.8. The flux ring according to claim 1, wherein said flux ring includes apair of magnets.
 9. A method of manufacturing a flux ring, comprising:providing a ring having an anchoring mechanism; placing said ring in adie; molding a first isotropic magnetic material onto said ring and saidanchoring mechanism securing said first isotropic magnetic material ontosaid ring; molding a second anisotropic magnetic material onto said ringadjacent said first isotropic magnetic material and said anchoringmechanism securing said second anisotropic magnetic material to saidring.
 10. The method according to claim 9, further comprising moldingsaid second anisotropic magnetic material on two sides of said firstisotropic magnetic material.
 11. The method according to claim 9,further comprising molding said first isotropic magnetic material underno magnetic field.
 12. The method according to claim 9, furthercomprising molding said second anisotropic magnetic material under amagnetic field of about 1400-1600 amp/meter.
 13. The method according toclaim 10, further comprising molding said first isotropic magneticmaterial along a portion of an arc circle of said ring, said portionbeing about 40° to 50°.
 14. The method according to claim 13, furthercomprising molding said second anisotropic magnetic material along saidarc circle such that said magnet covers about 140° of said circle.
 15. Amotor comprising: a stator assembly, said stator assembly including aflux ring comprising: at least one magnet on said ring, said at leastone magnet including a portion formed from an isotropic magneticmaterial and a portion formed from an anisotropic magnetic material; anarmature rotatable within said stator assembly; a commutator rotatablewith said armature and connected to said armature via a shaft; and brushassemblies associated with said commutator.
 16. The flux ring accordingto claim 15, wherein isotropic magnetic material being an isotropicmagnetic powder.
 17. The flux ring according to claim 15, wherein saidanisotropic magnetic material being an anisotropic magnetic powder. 18.The flux ring according to claim 15, wherein said isotropic magneticmaterial portion is sandwiched between two anisotropic magnetic materialportions.
 19. The flux ring according to claim 18, wherein saidisotropic magnetic material portion spans an arc circle of between 40°and 50° about said ring and said isotropic and two anisotropic magneticmaterial portions span about 140° about said ring.
 20. The flux ringaccording to claim 19, wherein said isotropic magnetic material islocated on one of the poles of a motor.
 21. The flux ring according toclaim 20, wherein one end is connected to said housing.
 22. The fluxring according to claim 15, wherein said flux ring includes a pair ofmagnets.
 23. A power tool comprising: a housing; a motor in saidhousing, said motor comprising: a stator assembly, said stator assemblyincluding a flux ring comprising: at least one magnet on said ring, saidat least one magnet including a portion formed from an isotropicmagnetic material and a portion formed from an anisotropic magneticmaterial; an armature rotatable within said stator assembly; acommutator rotatable with said armature and connected to said armaturevia a shaft; brush assemblies associated with said commutator; a powersupply; an output member coupled with said motor shaft; and an actuatormember electrically coupled between said motor and said power source forenergizing and de-energizing said motor which, in turn, rotates saidoutput member when said motor is energized.
 24. The flux ring accordingto claim 23, wherein isotropic magnetic material being an isotropicmagnetic powder.
 25. The flux ring according to claim 23, wherein saidanisotropic magnetic material being an anisotropic magnetic powder. 26.The flux ring according to claim 23, wherein said isotropic magneticmaterial portion is sandwiched between two anisotropic magnetic materialportions.
 27. The flux ring according to claim 26, wherein saidisotropic magnetic material portion spans an arc circle of between 40°and 50° about said ring and said isotropic and two anisotropic magneticmaterial portions span about 140° about said ring.
 28. The flux ringaccording to claim 27, wherein said isotropic magnetic material islocated on one of the poles of a motor.
 29. The flux ring according toclaim 28, wherein one end is connected to said housing.
 30. The fluxring according to claim 23, wherein said flux ring includes a pair ofmagnets.